fade_out

Apply a smooth cosine-squared fade to the last duration_s of the buffer. Composes with env for the common “long ring that needs a graceful tail” shape.

Signature

signal.fade_out(duration_s) -> Signal

• duration_s — length of the fade region, measured from the end of the buffer.

The first len(signal) − duration_s of the buffer is unchanged. Over the last duration_s the amplitude follows cos²(π·t/2) where t runs 0 → 1 — smooth at both ends (no audible kink where the fade begins, exact zero at the end).

When to use it

The single exponential env decays forever; if the buffer is shorter than the envelope’s natural die-off, the buffer terminates with the envelope still at audible amplitude and you hear a click on playback. You have two choices:

1. Extend the buffer until the envelope is inaudible — wasteful for long-ring sounds; you’re storing seconds of near-silent samples.
2. Use fade_out — keep the buffer as long as you actually want to hear the sound, and let fade_out mop up whatever amplitude is left at the end.

Example: long ring with graceful tail

patch("ping", "one_shot",
    sine(440.0, 2.5)
        .env(0.008, 1.2)            // body: slow exponential decay
        .fade_out(0.4));            // tail: smooth ramp to silence
                                    //       over the last 400 ms

The body envelope decays at its natural exponential rate; the fade catches whatever amplitude remains in the last 400 ms and brings it cleanly to zero.

Notes

• fade_out(duration_s) truncated to buffer length. Pass a duration_s bigger than the buffer and the entire buffer gets faded.
• fade_out(0) or negative is a no-op.
• The cosine-squared shape is the audio-engineering standard for clean fades. Linear fades have a perceptual “kink” where the slope changes; this one’s smooth all the way through.